Efficient Information Dissemination in VANETs

Abstract

In this chapter we gave an overview over possible VANET applications and showed different communication paradigms used for such applications. We also pointed out the importance of broadcast mechanisms for active safety applications. This was followed by an overview of the special network characteristics of VANETs. From that, we deduced a set of requirements for broadcast protocols which have to be fulfilled for a successful deployment of VANET applications. Also a classification of broadcast protocols was introduced which enables a more systematic analysis of broadcast mechanisms. Based on this, we have reviewed state-of-the-art broadcast protocols designed for inter vehicle communication. The main focus here was on hybrid protocols, which combine positive properties of more protocol classes and offer thereby promising characteristics for broadcast applications in vehicular networks. The theoretical evaluations were confirmed by extensive simulations. We have shown that deterministic protocols are heavily affected by node mobility and network load, and they are therefore not suitable for VANET applications. Furthermore, we have shown that pure flooding, as well as static gossip, is not scalable, i.e. they cause the so called broadcast storm problem. Thus, with increasing node density and network load their performance drop significantly and they are therefore unfeasible for VANETs. On the other hand, the RAAG achieves very promising results in sparse as well as in dense networks. We have shown that the message loss avoidance mechanism yields a significant performance gain in sparse scenarios and increases the robustness of the protocol also in dense networks. Moreover, RAAG is not affected by node mobility which is a very desirable property of VANET protocols. Thus we can conclude thatRAAGis predestinated for dynamic networks like VANETs and satisfies the requirements in such networks also in the presence of critical safety applications. Although the presented results are very promising, there are some issues we want to address in future work. First of all, RAAG requires 2-hop neighborhood information which generates more overhead.We aim to reduce this required knowledge to 1-hop neighbors, similar to the PbG protocol but in a more general way. Moreover, we have to evaluate the performance of RAAG in the presence of pseudonym changes, which may have a significant effect on broadcast protocols. Also a detailed evaluation of the message loss avoidance mechanism in partitioned networks and its optimization could result in a significant gain in delay-tolerant networking.